/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.solr.highlight;

import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.OffsetAttribute;
import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
import org.apache.lucene.search.highlight.Fragmenter;
import org.apache.lucene.search.highlight.NullFragmenter;
import org.apache.lucene.search.highlight.SimpleFragmenter;
import org.apache.solr.common.params.HighlightParams;
import org.apache.solr.common.params.SolrParams;

public class GapFragmenter extends HighlightingPluginBase implements
		SolrFragmenter {
	public Fragmenter getFragmenter(String fieldName, SolrParams params) {
		numRequests++;
		params = SolrParams.wrapDefaults(params, defaults);

		int fragsize = params.getFieldInt(fieldName, HighlightParams.FRAGSIZE,
				100);
		return (fragsize <= 0) ? new NullFragmenter()
				: new LuceneGapFragmenter(fragsize);
	}

	// /////////////////////////////////////////////////////////////////////
	// ////////////////////// SolrInfoMBeans methods ///////////////////////
	// /////////////////////////////////////////////////////////////////////

	@Override
	public String getDescription() {
		return "GapFragmenter";
	}

	@Override
	public String getSource() {
		return "$URL: https://svn.apache.org/repos/asf/lucene/dev/branches/lucene_solr_4_0/solr/core/src/java/org/apache/solr/highlight/GapFragmenter.java $";
	}
}

/**
 * A simple modification of SimpleFragmenter which additionally creates new
 * fragments when an unusually-large position increment is encountered (this
 * behaves much better in the presence of multi-valued fields).
 */
class LuceneGapFragmenter extends SimpleFragmenter {
	/**
	 * When a gap in term positions is observed that is at least this big, treat
	 * the gap as a fragment delimiter.
	 */
	public static final int INCREMENT_THRESHOLD = 50;
	protected int fragOffset = 0;

	private OffsetAttribute offsetAtt;
	private PositionIncrementAttribute posIncAtt;

	public LuceneGapFragmenter() {
	}

	public LuceneGapFragmenter(int fragsize) {
		super(fragsize);
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * org.apache.lucene.search.highlight.TextFragmenter#start(java.lang.String)
	 */
	@Override
	public void start(String originalText, TokenStream tokenStream) {
		offsetAtt = tokenStream.getAttribute(OffsetAttribute.class);
		posIncAtt = tokenStream.getAttribute(PositionIncrementAttribute.class);
		fragOffset = 0;
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * org.apache.lucene.search.highlight.TextFragmenter#isNewFragment(org.apache
	 * .lucene.analysis.Token)
	 */
	@Override
	public boolean isNewFragment() {
		int endOffset = offsetAtt.endOffset();
		boolean isNewFrag = endOffset >= fragOffset + getFragmentSize()
				|| posIncAtt.getPositionIncrement() > INCREMENT_THRESHOLD;
		if (isNewFrag) {
			fragOffset = endOffset;
		}
		return isNewFrag;
	}
}
